25570-45-0Relevant academic research and scientific papers
Structural Effects in Solvolytic Reactions. 43. Effect of Increasing Electron Demand on the 13C NMR Shifts for 2-Aryl-3-methyl-2-butyl Cations. A Static System Becoming an Equilibrating System with Electron-Withdrawing Substituents
Brown, Herbert C.,Periasamy, Mariappan
, p. 529 - 533 (1983)
A series of 2-aryl-3-methyl-2-butyl cations was prepared in SbF5/FSO3H/SO2ClF at -78 deg C and their 13C NMR shifts were measured at -80 deg C.A plot of the observed ΔδC+ values against the ?C+ constants gives a straight line for substituents over range p-OCH3 to m-Cl (slope ρC+ = -18.2, correlation coefficient r = 0.999).However, the data points for the strongly electron-withdrawing substutients, m-CF3, 3,5-Cl2, and p-CF3, deviate upward from this straight line.The ΔδCα/?αC+ plot for the α-methine (CH) carbon atom exhibits a linear correlation of the data points for derivatives with substituents p-OCH3 to m-Cl, with a downward deviation of the data points for derivatives containing strongly electron-withdrawing substituents.These results are in accord with a rapid 2,3-hydride shift in derivatives containing benzylic cations with higher energies.An increase in temperature from -80 deg C to -30 deg C causes enhanced deviations, in accord with a rapid equilibration that forms more of the less stable cations at the higher temperatures.In the case of 2-aryl-2-norbornyl cations, similar upward deviations are observed in the ΔδC+/?C+ plot.However, the spectra of these cations reveal no temperature dependence over the same temperature range.This indicates that equilibration is not the factor responsible for the deviation observed in the ΔδC+/?C+ plot for the substituted 2-aryl-2-norbornyl cations.
(5,6-Dihydro-1,4-dithiin-2-yl)methanol as a Versatile Allyl-Cation Equivalent in (3+2) Cycloaddition Reactions
Hullaert, Jan,Winne, Johan M.
supporting information, p. 13254 - 13258 (2016/10/30)
The title heterocyclic alcohol readily generates a sulfur-substituted allylic cation upon simple treatment with a protic acid, thus facilitating a synthetically useful stepwise (3+2) cycloaddition reaction pathway with a range of conjugated-olefin-type substrates. The introduction of an allyl fragment in this way provided rapid access to a variety of cyclopentanoid scaffolds. The cyclic nature of the cation precursor alcohol was shown to be instrumental for efficient cycloaddition reactions to take place, thus indicating an attractive strategy for controlling the reactivity of heteroatom-substituted allyl cations. The formal cycloaddition reaction is highly regio- and stereoselective and was also used for a short total synthesis of the natural product cuparene in racemic form through a cycloaddition–hydrodesulfurization sequence.
